1. Field of the Invention
This invention relates to a coupling assembly for transmitting rotational motion between a driving shaft and a driven shaft, and more particularly toward an Oldham-style coupling with reduced lash.
2. Related Art
In various power transmission configurations, rotating shafts are coupled to each other with a coupling joint to accommodate small amounts of shaft misalignment from collinearity. Such coupling devices have been proposed in a variety of configurations. One design of fairly ancient origin is the Oldham coupling, as shown in FIG. 7, wherein a center torsion block is provided with diametric slots on opposite faces that are oriented perpendicular to each other. Sliding of the center block permits a substantial amount of lateral shaft offset, while built-in clearance permits some angular misalignment as well.
A particular concern with such couplings can arise in certain applications where lash, i.e., clearance or play between contact faces, is undesirable. For example, vacuum pumps are used in some vehicular applications to assist operation of the brake system. For safety reasons, these vacuum pumps are not allowed to be driven from the front end accessory drive (FEAD) belt, and therefore are commonly driven from a timing chain, belt or gear from the cam shaft or other convenient power shaft. When driven from a cam shaft gear or timing gear, as an example, torsional vibrations inherent in the subsystem can introduce unwanted noise, vibration and harshness (NVH), as well as component wear.
The source of backlash in prior art style Oldham couplings (FIG. 7) is found at the interfaces between the drive lugs and the coupling plate slots. Because a slip fit condition is required to achieve proper sliding function and accommodate axial misalignment, lash necessarily exists in the prior art systems. Accordingly, there is a need to couple two rotary members having respective driving and driven shafts in close proximity while accommodating modest shaft misalignment, without introducing unwanted NVH or wear into the mechanical system. The terms “driving” and “driven” refer to the direction of power flow. A driving feature transmits torque to a driven feature in the same hand of rotation as the direction of rotation, whereas a driven member transmits torque to the driving member in a hand of rotation opposite to the direction of rotation.